US election: Barack Obama no longer the underdog as he pulls ahead of entire GOP field in new poll

Barack Obama has opened up polling leads against all of his potential
Republican challengers, as Americans grow more optimistic that their economy
is recovering and Mitt Romney's popularity declines while his bitter primary
contest continues.

The US president now stands at least six percentage points clear of each man who may be his opponent in November's election, according to the New York Times/CBS News poll. A month ago he was tied with Mr Romney, the Republican front-runner.

Nate Silver, the newspaper's in-house polling expert, said that while in November Mr Obama had been "a slight underdog to win re-election", the latest figures showed that "three months later, his position is much stronger".

The survey follows a series of positive economic indicators, including consecutive months of better-than-expected job creation figures. More than a third of Americans now believe that their economy is getting better, compared to 22 per cent who believe it is getting worse. Five months ago, pessimists outnumbered optimists by more than three to one.

However Mr Obama has not convinced voters that he should be credited with the burgeoning recovery. Half disapprove of his performance on the economy, compared to 44 per cent who approve. Meanwhile just 35 per cent of voters believe the country is "on the right track", while 59 per cent say it is not.

Yet the survey also reflected dissatisfaction towards the Republicanpresidential field. The poll found that just 34 per cent of Republican voters were satisfied with the current range of candidates, while 62 per cent wanted more options.

Trailing by six percentage points, Mr Romney remains Mr Obama's most formidable potential general election challenger. The president leads Rick Santorum by eight points in a hypothetical face-off, Ron Paul by 11 points and Newt Gingrich by 18.

However a string of polls show that the former Massachusetts governor's personal ratings are declining the longer he is engaged in a primary battle against rivals once dismissed as no-hopers.

He has slipped behind Mr Santorum, a Right-wing former Pennsylvania senator, among Republican voters nationwide, and faces a painful fight to win the party primary later this month in Michigan, his home state, where his father George was governor in the 1960s.

A Public Policy Polling survey puts Mr Santorum 15 points ahead in Michigan, which Mr Romney's team believes he must win. While his "net favourability" – the gap between the proportion of voters who like him and who do not – stands at just one per cent nationwide, Mr Santorum's is 42 per cent.

Restoring Our Future, the political action group allied to Mr Romney and credited with severely damaging the campaign of Mr Gingrich, a former House Speaker, has begun pouring millions of dollars into attack advertising against Mr Santorum in Michigan, Arizona and Ohio.